The invention relates to an electrical coil comprising a coil body, an exciting winding arranged on the coil body between flanges, and a jacket of insulating material arranged over the exciting winding. Furthermore, the invention relates to a method for producing such a coil.
In electrical coils, in particular for use in relays or similar switching apparatus, it is often desirable to protect the sensitive winding wires against damage from outside by means of a jacket. In addition thereto, such an enclosure of the coil also has the function of protecting the surroundings of the coil, and thus in particular the relay contacts, against outgassing from the varnish insulation of the winding wire.
DE 36 42 246, for example describes a method of enclosing a coil with insulating material, with the jacket being made by injection molding in a mold. This entails quite considerable expenditure since it does not only necessitate a mold and an injection molding machine, but this injection molding operation also needs to be provided for as a completely separate step in the manufacturing process.
It is the object of the invention to design a coil with a jacket, and to indicate a method of making the same, such that said jacket increases the coil diameter as little as possible only and can be made with low manufacturing expenditure.
According to the invention, this object is met with a coil of the type indicated at the outset in that the jacket is formed as a peripheral insulating winding having at least one winding layer of insulating fiber material, with the juxtaposed turns thereof being adhered to each other so as to form a continuous insulating layer.
The invention thus provides a jacket in the form of an additional winding using insulating fiber material which, upon winding of the exciting coil, is applied in the same manner and with the same winding machine in one layer or, if necessary, also in several layers on top of the exciting winding and is adhesively bonded together and also to the flanges, respectively. There is thus no additional expenditure whatsoever required for an injection molding machine and a casting mold, respectively.
The method according to the invention for producing such a coil consists in that, after winding of the exciting coil, an at least one-layer insulating winding of insulating fiber material is applied over the exciting winding and that the individual turns of the insulating winding are adhered to each other. Preferably, the insulating fiber proper may consist of thermoplastic material, with the possibility of melting on the fiber by a subsequent heat treatment so as to thereby adhere the individual turns to each other, or it is possible to use a mineral fiber which is impregnated with a casting resin, for example, a duromer resin and cured after winding. Depending on the type of the resin used, either automatic curing at room temperature or curing by heat treatment is feasible. In principle, it would also be conceivable to impregnate the fiber with resin only after the winding operation, with the resin then spreading through the fiber. However, this necessitates an additional step comprising metering of the resin as well as specific precautions to make sure that the resin really is distributed over the entire surface. In any case, by adhering the insulating winding according to the invention, a gastight enclosure over the copper/varnish wire winding is provided.